I. Technical Field
This invention generally relates to tube cutting apparatus of the type employed to sever sections of a continuous length of tubing or similar enlongated stock emanating from a source thereof such as a mill and in which a cut-off die set driven by a swinging ram assembly is clamped to the continuous length of tubing prior to and during the severing operation. More particularly, the present invention is directed to improvements in the tube clamping mechanism which allow simple, rapid adjustment of the die clamping jaws while eliminating possible damage to such mechanism when foreign objects become lodged between the jaws.
II. Description of the Prior Art
Tube cutting apparatus of the general type mentioned above is well known in the art as is exemplified by U.S. Pat. Nos. 3,938,415 and 4,108,029 owned by the assignee of the present invention, the entire disclosures of which patents are hereby incorporated by reference herein. While the prior art machines disclosed in these patents are both highly efficient and are well suited for their intended purpose, certain aspects thereof are nevertheless subject to improvement as will be discussed more fully hereinunder.
Tube clamping mechanism of the prior art machines noted above consists of a pair of opposed, complemental die jaws for clamping the tubing, which are removably mounted by bolts on corresponding, slidable die jaw holders or slides. A pair of opposing roller members forming cam followers are respectively rotatably mounted on the slides and are adapted to be slidably engaged and laterally displaced by a wedge cam carried by a vertically reciprocable ram assembly. Outward lateral displacement of the cam followers away from the cam produces closing of the die jaws to clamp the tubing. The clearance between the die jaws in their closed, clamping position is therefore directly dependent on the magnitude of displacement of the cam followers produced by the cam; more or less than the proper amount of die jaw clearance will result in the application of either too much or too little clamping force on the tubing. Inadequate clamping force may permit the tubing to twist within the jaws during the cutting process, thereby reducing the quality of the cut, while excessive clamping force may damage thin wall type tubing or may result in damage of certain components of the clamping mechanism itself.
Die jaw clearance is largely determined by the cumulative manufacturing tolerances of the various mechanical components which communicate force from the cam to the die jaws. While the tolerances of such components may be closely controlled during the manufacturing thereof in order to achieve a specific die jaw clearance, narrow manufacturing tolerances naturally increase production costs and therefore should desirably be maintained as broad as possible. In any event, wear on the components over an extended period of die increases the cumulative tolerance, thereby increasing die jaw clearance beyond an acceptable level.
Another problem sometimes experienced in connection with the prior art machines involves mechanical failure of the clamping mechanism in the event that foreign objects or articles become lodged between the die jaws upon closing thereof. It is not entirely uncommon, for example, for metal parts or shaving to be carried along with the advancing tubing into the die jaws; such foreign articles become wedged between the tubing and the die jaws when the latter are closed during the clamping sequence. In this case, the force loading imposed on the various components transmitting the clamping force from the cam to the jaws may result in mechanical failure thereof. Because the cam followers are provided in the form of rollers mounted on stationary axles, at least one of such axles usually shears away from its mounting on corresponding slide when the die jaws are "jammed" by a foreign article, thus requiring repair which necessitates shut down of the machine.
The die jaws associated with the prior art machines each consist of a pair of die jaw portions removably mounted on one of the slides. Each pair of die jaw portions includes essentially flat, opposing, spaced apart faces forming a slot through which the severing blade may pass during the cutting operation. Due to wear, the die jaw portions must be periodically removed from the machine and the opposed faces thereof reground to a smooth surface finish. Since the spacing between the opposing faces of the die jaw portions is relatively critical in achieving clean cuts, the die jaw portions are mounted for sliding adjustment on their slides in order that the die jaw portions may be moved closer together as material from the opposed faces thereof is removed during repeated grinding operations. The expedient previously resorted to for providing the necessary adjustability of the die jaw portions consists of elongating the base of each die jaw portion in order to accommodate an elongate slot and which is provided in such base. A stationary bolt trained through the slot is threadably received in the slide; in this manner, the die jaw portions are slidable toward and away from each other relative to the slide upon which they are mounted. Tightening of the adjustment bolts fixes the position of the die jaw portions on the slide. This approach to the problem of providing adjustment of the die jaw portions is less than completely satisfactory from a manufacturing standpoint however, since elongation of the base of each die jaw portion adds to the material cost of the machine.
As an improvement over prior art machines, one feature of the present invention resides in the provision of a means for rapidly and conveniently adjusting the clearance between the die jaws, which not only allows manufacturing tolerances of the individual components to be relaxed, but also compensates for wear of the components after an extended period of machine use. Moreover, the provision of a convenient means of adjusting the die jaw clearance readily permits altering die jaw pressure, which is especially useful in compensating for variations in the characteristics of the particular tubing being cut, such as minor variations in the outside diameter thereof.
Another significant aspect of the invention lies in the provision of a means of preventing excessive force from being communicated from the cam through the various clamping components to the die jaws; by this feature the necessity for replacement of components damaged by overload forces, and concomitant down time of the machine for repair are eliminated.
Finally, yet another aspect of the invention relates to novel means for adjustably mounting the die jaw portions on their slides in a manner which reduces the quantity of metal employed to form each of the die jaw portions.